# SOME OPERATIONS WITH NUMERICAL VECTORS AND LOGICAL VECTORS

x <- c(-5,0,7,-6,14,27)		# data vector x

x[1] 				# prints first element of x

x[length(x)]			# prints last element of x

x[i]				# the ith entry if 1<=i<=n, NA if i>n, all but
				#    the ith if -n<=i<=-1, an error if i < -n, and
				#    an empty vector if i=0

x[c(2,3)]			# the second and 3rd entries

x[-c(2,3)]			# all but the seccond and third entries

x[i] <- 5			# assign a value of 5 to the first entry;
				#    also can use x[i] = 5

x[c(1,4)] <- c(2,3)		# assign values to the first and fourth entries

x[indices] <- y			# assign to those indices indicated by the values
				#    of INDICES:  if y is not long enough, values
				#    are recycled; if y is too long, just its initial
				#    values are used and a warning is issued

x < 3				# vector with length n of TRUE or FALSE
				#     depending if x[i] < 3

which(x<3)			# which indices correspond to the TRUE values 
				#    of x<3

x[x<3]				# the x values when x<3 is TRUE -- same as x[which(x<3)]